Sales of mechanical exoskeletons cap decades of scientific tinkering that included a 680-kilogram General Electric clunker in the 1960s.

Strapped to users' bodies and powered by lithium-ion batteries, the emerging technology has led to some models that sell for about US$70,000, weigh less than 50 pounds and are nimble enough to dance the Macarena.

"We're now seeing a golden age in which we can produce this technology and derive benefit from it," said Keith Maxwell, business development manager for Lockheed's program. "There's a host of industries where this works."

The first commercial sale of a medical unit - not for lab or hospital tests - came in September, pioneering a field that may produce US$400 million in annual revenue by 2020, according to technology consultant ABI Research. Lockheed says it hasn't estimated the value of any contracts for its under-development military version, known by the acronym HULC, or for the nascent industrial market its Mantis device will enter this year.

MILITARY BOOST

The machines may follow a classic arc from Pentagon research project to fixture on an assembly line, similar to the development of lasers, said Paul Saffo, managing director of foresight at investment advisory firm Discern.

"The medical devices get the most attention, the military funds it and the first mass application is industrial," Saffo said.

Developing technology for both civilian and military use would be a boost for Lockheed, the world's largest defence contractor, as it confronts reductions in US arms spending. Parker Hannifin, the biggest manufacturer of motion and control devices, is seeking to expand into the medical industry.

Commercial exoskeletons are just echoes of Hollywood's take on Iron Man's bulletproof garb and the armour that Heinlein envisioned for his futuristic warriors.

Ekso Bionics' device for spinal patients looks like the lower half of a black metal skeleton able to stand by itself on foot pads. Parker Hannifin's medical model breaks into five pieces and resembles elongated, plastic football thigh pads worn on the sides of users' legs.

MOTORS, SENSORS

Electric motors amplify the strength in their wearers' limbs or, in the case of the wheelchair-bound, to supply motive power. Computers and sensors help provide balance and guidance.

"There's a huge wave of human augmentation coming," said Ekso Bionics chief executive Nathan Harding, whose California-based company has devices in operation at New York's Mount Sinai Hospital, the Kessler Institute for Rehabilitation in New Jersey and other spinal-cord injury centres. "It's in its infancy."

Argo Medical Technologies entered the market last year, with an exoskeleton to assist patients who have lost the use of their legs. Parker Hannifin's Indego model also targets those users, and will go on sale in 2014 at a price the company says is competitive with Argo's €2,00 unit.

In between those introductions will come Lockheed's Mantis, which the Bethesda, Maryland-based company envisions as finding a home in any industry in which workers must hold heavy equipment that can cause fatigue and back injuries.

MACARENA FOOTWORK

Mantis has a mechanical extension for a wearer's arm and absorbs the strain from hefting a grinder or sander, Maxwell said. Tests found productivity gains of more than 30 per cent, he said, and wearers showed their Macarena footwork to demonstrate the suits' flexibility.

"It turns workers away from being a weightlifter and into a craftsman," Maxwell said.

While Ekso Bionics' Harding sees exoskeletons on an evolutionary path toward ever-greater sophistication - much as so-called brick handsets in the early 1990s morphed into today's smartphones - it may not be that easy to cut costs, simplify the technology and ensure widespread adoption.

"Even though there are processors and sensors, there's still a lot of physical matter that has to be machined and built," said Discern's Saffo, who is also a consulting associate professor at Stanford University's engineering school.

BATTERY LIMITS

The other limitation is battery life. Batteries can be made only so powerful before turning into a bomb, Saffo said. Boeing knows the risks in working with larger versions of the lithium-ion cells found in mobile phones and other electronic gadgets: it's still trying to figure out the cause of electrical faults that grounded its 787 Dreamliner.

"Until you have higher-density power storage, you're always going to be looking for a plug for your exoskeleton," Saffo said.

The exoskeleton industry is attractive because the potential is vast and the large competitors are few, according to Lockheed and Parker Hannifin.

Back strain is the most common non-combat injury because of the heavy packs soldiers carry, Maxwell said. Lockheed licensed some technology from Ekso Bionics to produce the HULC, which is set to enter a second development phase this year as the system is refined so it can be worn under a uniform.

Exoskeletons hold "tremendous potential" to ease those burdens, said David Accetta, a spokesman for the US Army Natick Soldier Research, Development and Engineering Centre in Massachusetts. A field demonstration is planned for May, he said. Lockheed said the program hasn't been affected by mandated budget cuts that began on March 1.

Parker Hannifin, which has been working with Vanderbilt University in Nashville, Tennessee, is targeting Indego at the estimated 700,000 Americans with spinal cord injuries, said Achilleas Dorotheou, the program's business unit manager. Another pool of potential users: the estimated 600,000 stroke survivors, many who are left with difficulties walking, he said.

STARTING AGAIN

Michael Gore, 42, who hasn't walked on his own since falling 11 years ago from the mezzanine of a North Carolina vinyl-siding factory, has used an Indego exoskeleton to traverse uneven terrain and climb stairs. He has been testing the model since 2010 at the Shepherd Centre in Atlanta, a private, non-profit hospital specialising in spinal-cord injury treatment.

"It's just a big emotional high to be able to stand up and speak to people face-to-face, eye-to-eye, instead of having to look up all the time," Gore said.

For now, the devices still require the use of crutches to maintain balance, and people will probably use them in combination with wheelchairs, Dorotheou said.

Parker Hannifin is playing catch-up with Argo Medical, which was founded by Amit Goffer, an Israeli who was paralysed in a 1997 automobile accident. The Yokneam Illit, Israel-based company has sold about 65 medical exoskeletons, 20 of them to individuals in Europe.

Argo Medical still lacks federal clearance for US sales to individuals, and the company may offer a product with fewer features to speed approval, CEO Larry Jasinski said.

Insurance companies eventually may cover part of the tab for medical exoskeletons because of the health benefits of greater mobility, Jasinski said. Ailments from sitting for prolonged periods include bone loss, urinary-tract complications, pressure sores, diabetes and obesity, he said.

Gore, who played sports in high school and worked on the family farm before his fall, is eager to see prices drop and insurers decide that the expense of an exoskeleton outweighs the medical costs of keeping the disabled in wheelchairs.

"If insurance would help out and I had to borrow $10,000 or $15,000, I would do that," Gore said. "I would love to have one."